1. Field of Invention
This invention relates in general to incandescent vehicle lamps, and more specifically, to an efficient infrared radiation absorbing filter for an automotive lamp.
2. Background of Related Art
A lamp assembly for a vehicle typically includes a reflective housing enclosed by a transparent lens. A replaceable incandescent light source is coupled to a removable socket adjacent a rear reflective surface within the reflective housing. The illumination source extends into an interior space through an aperture formed in the rear of the reflective housing. The removable socket couples to the rear of the reflective housing for securing the removable socket and illumination light source to the lamp assembly.
The illumination light source emits radiation of all wavelengths. Short wave infrared radiation is the desirable radiation since short waves infrared radiation is within the visible range of light spectrum. Long wave infrared radiation is undesirable radiation since long wave infrared radiation is in the non-visible range of the light spectrum. For an illumination source such as a light bulb, only 5% to 10% of the total emitted radiation is visible light (i.e., short wave) and 90% to 95% is parasitic radiation (i.e., long wave) which only contributes to thermal heat and not light.
The heat generated by the long wave infrared radiation causes thermal management issues within the vehicle lamp assembly. Due to the heat generated by the long wave infrared radiation, lamp assemblies must be designed to thermally manage the heat. This typically includes added cost to the components of the lamp assembly for providing material that can withstand and manage the heat generated by the long wave radiation. Other issues involve design constraints which are the result of the heat generated. Heat reducing devices such as ventilators may be added to the lamp assembly but such devices require added cost. In addition, as the lamp cools and contracts, atmospheric air is drawn into the interior of lamp assembly as a vacuum thereby creating a passage for moisture and dust into the lamp assembly. Lamp assemblies are typically sealed components specifically to prevent any moisture or contaminants from entering the interior of the lamp assembly. Therefore, there is a need to reduce the heat generated by the illumination light fixture from reaching interior components within the lamp assembly without utilizing vents and the like.